This invention concerns an improvement to wide-belt sander machines.
There are many known examples of machines of this type which are used for finishing previously produced panels.
Currently the most commonly used structure for this type of machine consists of a supporting structure holding a conveyor belt for transporting workpieces in a longitudinal direction; a sanding device consisting of a series of rollers (usually a minimum of three and a maximum of five) with parallel axes, positioned cross-ways to and above the conveyor belt. These rollers carry a closed-loop sanding belt which is tensioned by the rollers in conjunction with hydraulic cylinders; the sanding belt is fitted with a device which presses it downwards in the direction of the conveyor belt. This device is positioned parallel to the rollers on the active section between the rollers and parallel to the longitudinal feed surface of the conveyor belt. This device consists of a cross-beam supporting a series of mobile plates, each of which is independent from the others, on an axis perpendicular to the conveyor belt. The said plates can oscillate where they make contact with the sanding belt thus making it possible to vary their angle with respect to the plane defined by the conveyor belt; the angle of the plates in relation to the workpiece entering the machine can thus be varied in order to enable different types of wood sanding: for example, by slightly accentuating the angle of the plates in relation to the conveyor belt it is possible to obtain harder sanding on the infeed side and gentler sanding on the outfeed side depending on the type of wood (wood with varying degrees of homogeneity), the type of sanding required, etc.
The machine described so far appears to be very reliable but during us constructional drawbacks have been noted: adjustment operations such as changing the angle of the plates are not easy for the user to carry out while other operations, such as changing the sanding belt require the operator to carry out complex manual operations. The positioning of the presser plates at a particular angle as specified by the user is in fact executed by the machine manufacturer before the machine is delivered; if the user subsequently wishes to alter the plate angle even slightly (for machining purposes) he must stop the machine for a certain period in order to allow the operator to position the plates at the new angle, something which was directly allowed for in the design stage; this operation is slow and difficult because it requires the dismantling of part of the cross-beam supporting the plates.
Changing the sanding belt, on the other hand, involves discharging the hydraulic pistons, in order to slacken the sanding belt, and the subsequent removal of the rollers from the machine support structure so that the operator can remove the worn sanding belt and fit a new one. Generally speaking the rollers are held to the machine frame by ring nuts running on threaded pins which in turn fit into seatings on the frame and into the roller axes; by unscrewing the ring nut the operator can remove the roller from the machine. Once again the operation with this type of device is slow and complicated; during transport from the manufacturer to the user the pins and ring nuts are removed from the machine and can easily be lost as a result.